1. Field of the Invention
The present invention relates to a method and apparatus for minimizing the escape of anesthetic gas into the atmosphere surrounding a patient being administered gaseous anesthesia. More particularly, the present invention is directed to a method and apparatus for collecting anesthetic gases that escape from an anesthetic mask adjacent the point at which they are introduced in order to minimize contamination of the ambient atmosphere with anesthetic gases.
2. Description of the Prior Art
The administration of anesthetic gases to a patient is frequently accomplished by means of a mask that is applied over the nose or the mouth, or both, of the patient in order to provide controlled introduction of the anesthetic gas to the patient without subjecting others around the patient to the direct flow of the gases. However, anesthetic gases frequently leak into and contaminate the atmosphere surrounding the patient, for a number of reasons, and thereby expose the anesthetist and others in the vicinity of the patient to those same anesthetic gases. Such leakage of anesthetic gas can be the result of leakage at the various joints and connections in the gas delivery system, the result of improper fit of the mask to the face of the patient, or the result of escape of gas by virtue of the periodic removal of the mask from the face of the patient to permit visual observation of the patient's nose and mouth, and thereby detect changes in color of the patient's lips and possible vomiting. All of those causes of leakage contribute to contamination by anesthetic gas of the atmosphere in the operating theatre. Such contamination exposes the anesthetist, the surgeons, and the nurses who are present in the operating theatre to those same anesthetic gases, which, even though in a less concentrated form, could, over a period of time, impair their effectiveness.
The National Institute of Occupational Safety and Health has recognized the possible adverse effects on anesthetists and others of extended exposure to anesthetic-contaminated air and has recommended an upper limit for the amount of such anesthetics in the operating theatre atmosphere. For example, tests have shown that the concentration of nitrous oxide anesthesia in the immediate breathing zone of the anesthetist in an operating theatre could range from 45 to 500 ppm, with a mean value of 145+/-29 ppm, by using a conventional anesthesia mask. The NIOSH has recommended an upper limit of 25 ppm. In that connection, the ordinary air conditioning and ventilation system in hospital operating rooms is insufficient to control the anesthesia level in the atmosphere to that level, particularly in the localized area in the immediate vicinity of the patient and anesthetist. Consequently, it has been suggested that a local gas collection system be utilized, wherein a nozzle or collector is placed close to the patient's face and is connected to an evacuation fan to withdraw the anesthesia gases that have escaped. However, because access to the patient's face from above must be maintained, such systems place the collection nozzle on the side of the patient's face, where they are relatively ineffective. Additionally, the proposed systems have been found to be quite bulky, and their installation costs are high.
Another approach to minimizing the escape into the atmosphere of anesthetic gases is to provide a double wall mask wherein the space between the walls is connected with a source of vacuum and defines an extraction passageway to collect and remove anesthetic gas that escapes between the inner mask and the face of the patient, as shown in U.S. Pat. No. 4,015,598, granted on Apr. 1, 1977, to Glenn E. Brown. However, the structure therein disclosed is of limited utility in that it collects anesthetic gas that leaks out between the inner mask and the patient's face, but it does not prevent the excessive escape into the atmosphere of anesthetic gas when the mask is removed from the patient's face, as is done periodically to check the patient and monitor his breathing.
There is, thus, a need for an improved means for preventing the escape into the surrounding atmosphere of anesthetic gases that are used in operating rooms in order to prevent the exposure of operating room personnel to excessively high levels of the anesthetics.